作者Honor1984 (奈何上天造化弄人？)
看板Math
标题Re: [中学] 高中一题数列与级数问题
时间Mon Oct 26 17:59:43 2020
※ 引述《yizihappyQ (Ms.Q)》之铭言：
: 请问这题要怎麽解？谢谢
: https://i.imgur.com/I0xzPTa.jpg
[(a_n + 2)/2]^2 = 2S_n
8S_n = (a_n + 2)^2
8a_1 = (a_1 + 2)^2 => a_1 = 2
8a_n = (a_n + 2)^2 - [a_(n-1) + 2]^2
=> (a_n - 2)^2 = [a_(n-1) + 2]^2
由题设知
=> a_n = a_(n-1) + 4
=> a_2015 = 2 + 4 * 2014 = 8058
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1F：推 hwanger : Neat 10/26 18:01
2F：推 yizihappyQ : 谢谢 10/28 14:51